Adjustable time delays are introduced into optical signals that are present in a variety of optical networks and systems. For example, delays of the optical signals within routers, switches and multiplexers may be adjusted to equalize propagation path lengths for the purpose of synchronizing signals within an optical network. Alternatively, progressively adjusted time delays introduced to the optical signals within sampling systems, such as equivalent time oscilloscopes, enable high-bandwidth signals to be accurately represented by the systems. Adjusting the delays of the optical signals in these networks and systems is achieved using variable optical delay elements.
Variable optical delay elements, such as the ODL-320/620 optical delay line module available from SANTEC Corp., use a pair of fiber collimators and a reflection mirror to introduce adjustable time delays to applied optical signals. These types of variable optical delay elements introduce precisely-controllable time delays, but have a narrow adjustment range, for example, from 0 to 300 picoseconds. Widening the adjustment range of this type of variable optical delay element requires increasing the propagation path length of the optical signals within the delay element. However, increasing the propagation length causes the physical dimensions of the delay element to correspondingly increase. Other types of variable optical delay elements, such as those based on index varying materials, or pivoting high-index slabs, are physically compact but they also have narrow delay adjustment ranges. There is a need for a physically compact variable optical delay element that introduces time delays to an applied optical signal over a wide adjustment range.